It is often desirable in a polymer-coatings application that a thermoset coating composition possess not only relatively high hardness and scratch resistance but also a relatively high degree of flexibility and impact resistance. Unfortunately, in a typical "coatings" polymer of this type, some of the parameters that control these physical properties seem to be undesirably linked. For example, when certain process variables are selectably controlled so as to produce a thermoset coating composition possessing acceptable or desired hardness and scratch resistance, such a polymer generally possesses little, if any, flexibility and impact resistance--which is of course undesirable and, in some applications, totally unacceptable. In contradistinction, a polymer that is produced so as to possess desirable flexibility and impact-resistance values typically also possesses an unacceptable hardness and/or scratch-resistance values. It is currently believed that conventional manufacturing processes cause these physical properties to be so related.
Briefly, conventional manufacturing processes can be summarized as follows. Polymeric thermoset coating compositions that can be utilized in a polymer-coatings application are typically produced from selected monomers, utilizing a series of steps. Specifically, such a polymer often comprises a main chain, and typically includes side chains attached to the main chain. The main chain and side chains, in particular, are furthermore typically formed at different times via separate reaction mechanisms, often utilizing separate reaction equipment to produce the desired polymer. U.S. Pat. Nos. 3,892,714 and 4,005,155, both to Sampson et al., disclose processes that are fairly typical of such a reaction scheme.
However, from an engineering, capital-investment, manpower, equipment-scheduling, and product-manufacturing standpoint, it would be not only desirable but also economical to effect the main-chain and the side-chain formations of such a polymer, utilizing a one-step reaction scheme.
Furthermore, it is also fairly typical, in conventional polymer coatings-manufacturing processes such as those processes mentioned above, to utilize a catalyst to effect the main-chain and/or the side-chain formation of the desired polymer product. (See, e.g., U.S. Pat. Nos. 3,892,714 and 4,005,155.)
One disadvantage of utilizing a catalyst to effect a one-step reaction is that the catalyst, which is typically utilized to effect the side-chain polymerization reaction, if also present when the main-chain polymerization reaction takes place, can undesirably interfere with the main-chain polymerization reaction. This, in turn, may result in the production of a polymer having undesirable properties, or may result in the production of an undesirable polymerization by-product that needs to be separated from the desired polymer product.
The catalyst that is utilized to effect side-chain polymerization, moreover, may cause transesterification, at the main-chain portion of the polymer, resulting in crosslinking during the polymerization process. This is undesirable because crosslinking tends to increase the viscosity of the thus-produced polymer solution, and may even result in the gellation of the polymer product or products so produced.
It would therefore further be desirable not only to produce such polymer products utilizing a one-step reaction scheme but also to be able to produce such polymer products without requiring the presence of a catalyst to do so.
We have discovered that a polymer of this type can be produced in a one-step reaction scheme which utilizes, for example, a single reaction vessel, while the main chain and side chains of such polymer are being formed simultaneously. In particular, we have discovered that a one-step reaction scheme--involving at least two reactions that take place substantially simultaneously--can be utilized to produce such a polymer.
We have also discovered that this dual-reaction mechanism can proceed without need of a catalyst.
Surprisingly, we have further discovered that by selectively controlling certain variables of the instant polymerization process we are able to produce a polymeric thermoset coating possessing not only relatively high hardness and scratch resistance but also a relatively high degree of flexibility, resiliency, and impact resistance as well.